Yea, I think this is an interesting approach. But FreePDK45 slides mention that it's not designed for manufacture, and there does not appear to be an easy upgrade path. So you could design a chip with FreePDK, release the design, and then redo the whole thing in a vendor PDK.

I talked to someone who worked on AsicOne, and he said that even if you make your own PDK and draw your own transistors and everything, you'll still have to sign an NDK to do the sign-off and what not. I'm not intimately familiar with the whole process myself, but from what I understand it is basically impossible to have an open source analog design that you can actually manufacture. (sure, you can make a theoretical toy thing, but if you can't manufacture it, who cares?)